A four year study was made of the effectiveness of a chemistry preparatory course (Chemistry 51) on students' success in general chemistry (Chemistry 1A-1B) in the three colleges of the San Mateo County Community College District (California). Data indicated: (1) approximately 60% of the students enrolled in Chemistry 51 completed the course, and of these, approximately 25% subsequently enrolled in Chemistry 1A and approximately 18% enrolled in Chemistry 1B; (2) Chemistry 51 grades were reliable indicators of Chemistry 1A performance; (3) Chemistry 51 graduates appeared to perform equally with those students enrolled directly into Chemistry 1A and 1B; (4) repeating students constituted 7.6% of Chemistry 51 enrollment, and over half of these repeaters withdrew from the course; (5) 96 students transferred from one college to another while taking the three course sequence, and appeared to maintain their level of performance. These courses were taught in the traditional lecture-discussion mode, with laboratory work included. The majority of the students enrolled in Chemistry 51 had no chemistry background and were inadequately prepared in mathematics and communication skills. (LH)